The present invention relates to a knocking detection device for detecting knocking of an engine mounted on a vehicle by directly converting an output of a knock sensor from an analog waveform into digital data.
A recent vehicle has a knocking controller with a knock sensor for detecting the knocking in dependency on abnormal combustion of the automotive engine to prevent the knocking by controlling an ignition timing. The controller is capable of controlling the ignition timing at a knocking limit, so that it is possible to improve power performance of the engine.
The knock sensor is provided at a suitable place to detect pressure vibration in a combustion chamber due to abnormal combustion or mechanical vibration transmitted from the combustion chamber to a cylinder block of the engine.
The determination for occurrence of knocking is disclosed in Japanese Patent Application Laid-open No. 58-30477 (1983) and No. 61-8472 (1986). Thus, a conventional knocking detection device comprises a knock sensor, a filter circuit for selecting a knocking component by limiting a frequency band of signals from the sensor, a peak hold circuit for holding a peak value of signal waveforms, and an analog/digital converter for converting the peak value from analog signal to digital signal. A microcomputer calculates an average value of a plurality of peak values from the converted digital signals and determines whether the knocking occurs or not by comparing the average value with a predetermined value of a knocking determination level.
However, analog circuits such as the filter circuit and the peak hold circuit in the conventional device use elements such as resistors and capacitors respectively having tolerance, so that it is impossible to avoid an error depending on a circuit constant. Every element is selected to set the circuit constant properly, which has many production steps. Many steps and the number of parts of the elements used in the analog circuits increase the production cost.
Furthermore, the elements deteriorate with lapse of time and the circuit characteristics change. Accordingly, the reliability of the analog circuits decreases.